weather

The boundaries between two air masses of different temperature and humidity. A warm front occurs when warm air displaces cold air; if cold air replaces warm air, it is a cold front.

Maximum and minimum thermometers are universally used in weather-reporting stations. The maximum thermometer, shown here, includes a magnet that fits tightly inside a capillary tube and is moved up the tube by the rising mercury. When the temperature falls, the magnet remains in position, thus enabling the maximum temperature to be recorded.

During World War II it was essential for the Royal Air Force to have the most accurate meteorological – and specifically high-altitude – information possible, before the pilots took off on their dangerous missions. It was one of many jobs that were entrusted to women during wartime. Precedents were set for the involvement of women in a wide variety of industries, including meteorology and weather forecasting, in the following years.

Variation of atmospheric conditions at any one place over a short period of time. Such conditions include humidity, precipitation, temperature, cloud cover, visibility, and wind. Weather differs from climate in that the latter is a composite of the average weather conditions of a locality or region over a long period of time (at least 30 years). Meteorology is the study of short-term weather patterns and data within a particular area; climatology is the study of weather over longer timescales on a zonal or global basis. Weather forecasts are based on current meterological data, and predict likely weather for a particular area.